[CMake] Fix LLVM build non-determinism on RHEL

On RHEL, the OS tooling (ar, ranlib) is not deterministic by default.
Therefore, we cannot get bit-for-bit identical builds.

The goal of this patch is that it adds the flags required to force determinism.

Differential Revision: https://reviews.llvm.org/D64817

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -135,6 +135,28 @@ if(APPLE)
   set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -Wl,-flat_namespace -Wl,-undefined -Wl,suppress")
 endif()
 
+if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
+  # RHEL7 has ar and ranlib being non-deterministic by default. The D flag forces determinism,
+  # however only GNU version of ar and ranlib (2.27) have this option. 
+  # RHEL DTS7 is also affected by this, which uses GNU binutils 2.28
+  execute_process(COMMAND ${CMAKE_AR} rD t.a
+                  WORKING_DIRECTORY ${CMAKE_BINARY_DIR} RESULT_VARIABLE AR_RESULT OUTPUT_VARIABLE RANLIB_OUTPUT)
+  if(${AR_RESULT} EQUAL 0)
+    execute_process(COMMAND ${CMAKE_RANLIB} -D t.a
+                    WORKING_DIRECTORY ${CMAKE_BINARY_DIR} RESULT_VARIABLE RANLIB_RESULT OUTPUT_VARIABLE RANLIB_OUTPUT)
+    if(${RANLIB_RESULT} EQUAL 0)
+      set(CMAKE_C_ARCHIVE_CREATE "<CMAKE_AR> Dqc <TARGET> <LINK_FLAGS> <OBJECTS>")
+      set(CMAKE_C_ARCHIVE_APPEND "<CMAKE_AR> Dq  <TARGET> <LINK_FLAGS> <OBJECTS>")
+      set(CMAKE_C_ARCHIVE_FINISH "<CMAKE_RANLIB> -D <TARGET>")
+
+      set(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> Dqc <TARGET> <LINK_FLAGS> <OBJECTS>")
+      set(CMAKE_CXX_ARCHIVE_APPEND "<CMAKE_AR> Dq  <TARGET> <LINK_FLAGS> <OBJECTS>")
+      set(CMAKE_CXX_ARCHIVE_FINISH "<CMAKE_RANLIB> -D <TARGET>")
+    endif()
+    file(REMOVE ${CMAKE_BINARY_DIR}/t.a)
+  endif()
+endif()
+
 if(${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   if(NOT LLVM_BUILD_32_BITS)
     if (CMAKE_CXX_COMPILER_ID MATCHES "XL")